It is well known that when particles of a metal become smaller than about 100 nanometers (nm) their characteristics, e.g., electronic structure, lattice specific heat, spin magnetic susceptibility and the like, become quite different from those of the bulk metal. Metal particles can be used in colored glasses and glass filters prepared by dispersing ultrafine particles of gold, silver or a semiconductor, e.g., CdS.sub.x Se.sub.1-x, in glass. These colored glass filters are known to have non-linear optical characteristics and can be used in optical switches and electronic devices for optical computers. The non-linear optical characteristics are attributed to the increase in third order non-linear optical characteristics caused by the band filling effect or the exciton confinement effect, which in turn is caused by the discreetness of energy bands due to the quantum confinement effect.
The glass having the particles dispersed therein can be made by a number of known methods. The sol-gel process includes the steps of adding colloidal metallic particles to a silica sol prepared by hydrolysis of a silicon alkoxide, dispersing the metallic particles, pouting the dispersion into a vessel, allowing it to gel, drying the gel and sintering the dried gel. The sol-gel process not only takes a very long time to produce the glass but difficulties are encountered in preventing colloidal metallic particles from aggregating. Also, this process has a serious disadvantage in that a high particle concentration cannot be achieved.
An alternative process is a sol-gel-combustion process that includes the steps of dispersing fine particles of a semi-conductor, e.g., silicon, in a sol prepared from alkoxide, drying the sol, permitting the sol to gel, sintering the gel and mixing the so-obtained semi-conductor fine particles (coated with an oxide glass) with fine glass particles formed by burning gaseous hydrogen and oxygen in the presence of a raw material for glass, e.g., SiCl.sub.4, GeCl.sub.4 and PCl.sub.3, with the gasses being continuously supplied, and then firing the mixture. The sol-gel-combustion process has difficulties in obtaining a high concentration of fine metallic particles.
Other alternative processes are the precipitation process and the sputtering process. In the precipitation process, the fine particles are precipitated in glass by maintaining a molten glass containing, e.g., CdSe, at a temperature not higher than its flowing temperature and not lower than its yielding temperature. The sputtering process includes the steps of preparing a composite glass by sintering a mixture of a low melting glass powder and a powder containing at least one of a cadmium source, sulfur source, selenium source or tellurium source, and then forming a fine particle dispersed glass by means of sputtering using the composite glass as the target. It is difficult to control the size of the fine metallic particles and to obtain a high concentration of fine metallic particles using either the deposition process or the sputtering process.
The ion implantation method implants metallic ions in a glass base by causing the ions to impact the glass base at a high speed and then heat treating to control the particle size. Large equipment that is unsuitable for mass production is required to use the ion implantation method. Furthermore, a high particle concentration cannot be achieved.
The materials used in these conventional methods are low in third order non-linear susceptibility [.chi.(3)] because of their low fine metal particle concentration. Increasing the fine metal particle concentration increases the third order non-linear susceptibility.
Materials having a large third order non-linear susceptibility can make optically bi-stable responses to a relatively small incident light intensity and enable not only high-density electronic component mounting but also rapid switching responses. Therefore, it is desirable to obtain a high fine metal particle concentration and have a large third order non-linear susceptibility.
A confined exciton is presently theorized to impart the non-linear characteristics to ultrafine particles of a semi-conductor material. The radius of the confined exciton is about 3 to about 4 times the semi-conducting material's Bohr radius. A well studied material is CdS-CdSe and its ultrafine particles are several tens of nanometers in size. In spite of the advantages of this material in ultrafine particle form, its Bohr radius is several nanometers which results in a limited number of confined excitons.
To make full use of the advantages of an ultrafine particle by obtaining many more confined excitons, a semi-conductor material having a smaller Bohr radius is desired. Two semi-conductor materials that have been studied are CuBr (having a Bohr radius of about 1.25 nm) and CuCl (having a Bohr radius of about 0.7 nm). Another semi-conductor material is Cu.sub.2 O (having a Bohr radius of 0.7 nm). Unfortunately, the copper is liable to undergo a reaction in the glass to form CuO, Cu.sup.++, Cu.sup.+ or Cu. It is conventionally impossible to obtain a glassy material that contains separated ultrafine Cu.sub.2 O particles dispersed therein at high concentrations.
A glassy material having a high ultrafine particle concentration, a large third order non-linear susceptibility and that uses particles having a small Bohr radius and which does not exhibit the above-described shortcomings is highly desirable. A method of making the glassy material that does not exhibit the shortcomings of the above-described methods is also desirable.